Abstract: During the use of organic pigments, it is required to have fine particle size and uniform particle size distribution, which requires grinding and dispersing of organic pigments. Taking the difficult-to-disperse phthalocyanine green pigment as an example, various factors affecting the grinding and dispersing effect were discussed, and a good grinding and dispersing process condition for this pigment was determined, and this process condition was applied to the grinding and dispersing of Orange-43 pigment. Also achieved good results.
0 Preface
Organic pigments are dispersed and colored in the base material used in the form of particles. In order to give full play to the performance of pigments such as tinting strength, vividness, and gloss, it is necessary to disperse the pigment particles in the base material in a fine, uniform, and stable state as much as possible. Commercially available pigments are often in the form of powder aggregates, and the particle size of the particles reaches hundreds of microns. It is necessary to use physical or chemical methods before use to make the pigment particles finer, control them within the required particle size range, and To achieve the purpose of dispersion.
In the production, the method of mechanical grinding and dispersion is usually used to make the pigment particles finer. In this method, there are many factors that affect the grinding and dispersing effect. It is helpful to improve the grinding efficiency and the dispersing effect by clarifying the role of each factor, and each factor itself has a certain allowable range. A range will have the opposite effect. Therefore, on the basis of experiments, this paper takes the dispersion of difficult-to-disperse phthalocyanine green pigments in water-based systems as an example, and discusses the factors that affect the dispersion of grinding.
1 Experimental part
1.1 Raw materials
Phthalocyanine green pigment, untreated; orange-43 pigment, untreated; dispersant Hydropalat 3275 (No. 1), Hydropalat 1080 (No. 2), Colorsperse 188A (No. 3), industrial products, Henkel Group; absolute ethanol, Analytical pure.
1.2 Experimental method
1.2.1 Grinding
Dry the untreated pigment first, pre-grind it in a mortar for a certain period of time, then weigh a certain amount of pigment and mix it with an appropriate amount of ethanol, and use a multipurpose SFJ-400 sand mill disperser at a fixed speed of 1 000 r/min. grind. Different pigment dispersions were prepared by changing the grinding time, the type of dispersant, the amount of dispersant and other conditions. The resulting dispersion was suction filtered, dried and ground.
1.2.2 Decentralization
Take 1.0 g of the pigment prepared above, add 50 mL of distilled water and stir to disperse. Change the dispersion time, dispersion temperature and other conditions to prepare the pigment aqueous dispersion.
1.3 Test method
1.3.1 Pigment dispersion test
Take 5 mL of the above pigment aqueous dispersion, put it in a centrifuge test tube, and centrifuge at 2000 r/min for 15 min, then use a graduated syringe to absorb the clear liquid at 2 cm below the liquid surface, and use a UV-visible Spectrophotometer at Measure its light transmittance at the maximum absorption wavelength, and calculate its dispersion:
Dispersion=1-light transmittance
1.3.2 Pigment dispersion stability test
Take the above-mentioned aqueous pigment dispersion, put it in a 15 mL graduated test tube, let it stand for 0.5 h, 1 h, 2 h, 4 h, 8 h, 12 h... After that, draw up the liquid surface with a graduated syringe. 2 cm below the supernatant to measure its dispersibility.
1.3.3 Microscopic analysis of pigment surface
After the pigment dispersion was fully dispersed in water by ultrasonic waves, it was dropped on the cover glass, coated with gold film, and put into a scanning electron microscope for observation.
2 Results and discussion
2.1 Effect of grinding time
The degree of dispersion of the pigment affects the optical properties of the pigment system. The absorption spectrum of the system can be measured with a UV-visible Spectrophotometer to determine the degree of dispersion and particle size change of the pigment. During the grinding process of the pigment, 1 mL of the grinding solution was taken out at different times and diluted to 10 mL with water. The measured absorption spectrum is shown in Figure 1.
Fig.1 Variation of dispersibility with grinding time
It can be seen from Figure 1 that the value of the absorption peak increases with the prolongation of the grinding time, indicating that the particle size of the pigment is decreasing and the dispersibility is gradually improved; when the grinding time reaches 2 h, the value of the absorption peak is almost unchanged, and the particle size of the pigment The distribution is balanced. This shows that under certain conditions, prolonging the grinding time can make the pigment particles smaller, but when a certain particle size is reached, due to the limitation of the grinding mechanism itself, it is meaningless to prolong the grinding time. Therefore, the appropriate grinding time should be selected when the particle size distribution of the pigment is balanced. Under the experimental conditions, the grinding time was determined to be 2 h.
2.2 Effect of dispersant
The dispersion of organic pigments includes three processes: the air adsorbed on the surface of the pigment particles is replaced by the dispersion medium, that is, the wetting process; the pigment aggregates are broken under the action of mechanical force to form primary particles or smaller aggregates, that is, mechanical pulverization and dispersion. Process; prevent the re-agglomeration of dispersed pigment particles or smaller aggregates, that is, the stabilization process. Therefore, dispersant is a necessary condition for wet grinding. In the experiment, three kinds of dispersants (No. 1, No. 2 and No. 3) were selected, and their dosages were all 10% of the pigment dosage. According to the aforementioned method, the dispersibility of the measured pigment is shown in Table 1.
由表 1 可见 ,3 种分散剂对颜料的分散性都有一定的改善 ,尤其是 1 号分散剂(亲水嵌段共聚物)分散性更好。故以下实验均选择 1 号分散剂 。
2.3 分散剂用量的影响
改变分散剂的用量(相对颜料量), 测定颜料分散性,结果见图 2。
图 2 分散性随分散剂用量变化图
由图 2 可见 ,当分散剂的用量从 5 %增加到 40 %时 ,颜料分散体系的分散性达到最大值。随着分散剂用量的进一步增加,其分散性反而下降。造成这种现象的原因在于 ,开始随着分散剂用量的增加, 越来越多的颜料粒子表面充分吸附分散剂 ,直至其表面的单分子层达到饱和 ,这时分散剂分子的碳氢链的空间位阻作用起到了很好的分散效果 。当分散剂用量进一步增加时 ,有可能使其在颜料表面相互缠结, 从而降低其分散性 。另外,介质在较厚分散剂的表面上滑动并不能有效研磨颜料粒子 ,使得研磨效率降低 。颜料在研磨分散过程中,分散剂的用量应适中 。本实验选择分散剂的用量为 40%。
2.4 分散温度的影响
改变分散介质的温度 ,考察样品的分散性, 结果见表 2。
表 2 分散温度对分散性的影响
以分散性对分散温度作图 ,见图 3
图 3 分散性随分散温度变化图
由图 3 和表 2 可见, 随着分散介质温度的升高 ,颜料体系的分散性逐渐变差,这主要是由于温度的升高 ,造成了分散剂的脱落, 从而使得体系的分散性变差 。确定很好的的分散温度为室温。
2.5 分散时间的影响
选取不同的分散时间 ,测定样品的分散性, 结果见图 4。
图 4 分散性随分散时间变化图
由图 4 可见 ,颜料分散体系的分散性受分散时间的影响 。本实验中,分散时间以 1 h 为宜。
2.6 产品性能测试
2.6.1 颜料处理前后分散稳定性比较
颜料经研磨 、分散剂处理后的分散稳定性与未处理颜料的分散稳定性进行比较 ,结果见图 5。
图 5 酞菁绿颜料处理前后分散稳定性比较
由图 5 可见 ,处理的颜料的分散稳定性较未处理的颜料有了较大的改善。
2.6.2 颜料分散体系的微观分析
用扫描电镜对未分散颜料和分散颜料进行观察,结果见图 6
图 6 酞菁绿颜料粒子的 TEM 照片(1 000X)
由图 6 可见 ,分散后的颜料呈孤立的原生粒子形态,而未分散处理的颜料是原生粒子的聚集体 。说明颜料研磨、分散剂的处理阻止了颜料粒子的聚集, 增加了颜料粒子在分散介质中的稳定性。
2.7 橙-43 颜料的研磨分散
将酞菁绿颜料研磨分散的很好的工艺条件用于橙-43颜料上 ,处理前后颜料的分散稳定性比较见表 3。
以分散性对沉降时间作图 ,见图 7 。
图7 橙-43 颜料处理前后分散稳定性比较
由图 7 和表 3 可见,采用确定的很好的研磨分散工艺条件对橙 -43 颜料进行处理 ,同样得到了良好的分散效果。
3 结 语
实验表明 , 有机颜料的研磨分散受研磨时间、分散剂种类和用量、分散温度、分散时间等多种因素影响 。在实验条件下, 选用亲水嵌段聚合物分散剂 , 用量为颜料量的 40%, 研磨时间 2 h, 在室温下分散1 h ,对酞菁绿颜料和橙 -43 颜料进行处理 , 可使其在水中的分散性有较大的改善 。
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